Add ESP8266, ESP32-C6, ESP32-C2, ESP32-H2 to chip selector with optgroup layout. Generalize UI text from ESP32-S3-specific to board-agnostic. Add esptool merge_bin examples for ESP32, ESP32-S3, and ESP8266. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>